dirty_d
10 kW
No. :lol:safe said:
Battery Testers (to check for low current)
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dirty_d
10 kW
you really over-thinking it, the extra current doesn't come from any voltage drop, the reason that there can be more current on the output side of the buck converter is that during the on-cycle some of the energy from the battery causes a current rise through the motor and the rest of the energy is stored in the magnetic field of the inductor(windings), in the off cycle no more current is going through the battery, but the magnetic field around the windings collapses and keeps the current flowing through the motor and through a flyback diode or timed switch. so for a 50% duty cycle you have current going through the battery half the time and current going through the motor all of the time, so there is half as much current through the batteries as the motor. now the reason that the voltage is 50% of the battery voltage is that when the battery forces current through the inductor half of the batteries voltage is dropped across the inductor so you are left with half of the battery voltage at the output, same when the inductor discharges.
Hey, I thought this was about battery testing . . .
In short, you get what you pay for. The $10 load tester from HF is a good tool - I've got one, and use it exactly what it is made for: load testing batteries.
Like most tools, it's value increases with experience. Put a (relatively) fixed load on a battery, and watch the voltage drop over time - a short time, maybe 5 to 30 seconds, depending. Do this with good, bad, and indifferent batteries and you'll get an idea of the batteries health. The more you do this, the better your estimation will be.
It does have drawbacks:
The analog voltmeter has poor resolution.
Use depends on experience, and is somewhat subjective.
Load is not adjustable.
Functionality is very limited.
Can I beat it? Yes. HF sells crappy (err, very inexpensive) multimeters for $3 - I've got one of these, too (as well as very high end Fluke and Tektronix gear). Check voltage with much better resolution, watch charger set points, get continuity, measure resistance - way more function for 1/3 the money, if money is your major measure. Can't beat this tool for price performance - how could you not have one of these in the toolbox for $3?
Shoot your wad, and buy both. Just as there is experience "in the real world", there is equally valuable experience to be had in the measurement world. Live in both worlds, and gain understanding in both - they are not mutually exclusive.
In short, you get what you pay for. The $10 load tester from HF is a good tool - I've got one, and use it exactly what it is made for: load testing batteries.
Like most tools, it's value increases with experience. Put a (relatively) fixed load on a battery, and watch the voltage drop over time - a short time, maybe 5 to 30 seconds, depending. Do this with good, bad, and indifferent batteries and you'll get an idea of the batteries health. The more you do this, the better your estimation will be.
It does have drawbacks:
The analog voltmeter has poor resolution.
Use depends on experience, and is somewhat subjective.
Load is not adjustable.
Functionality is very limited.
Can I beat it? Yes. HF sells crappy (err, very inexpensive) multimeters for $3 - I've got one of these, too (as well as very high end Fluke and Tektronix gear). Check voltage with much better resolution, watch charger set points, get continuity, measure resistance - way more function for 1/3 the money, if money is your major measure. Can't beat this tool for price performance - how could you not have one of these in the toolbox for $3?
Shoot your wad, and buy both. Just as there is experience "in the real world", there is equally valuable experience to be had in the measurement world. Live in both worlds, and gain understanding in both - they are not mutually exclusive.
Another thought on measuring batteries. If you have one of those little inverters (or know someone who does) with a low voltage disconnect, do this:
Plug in a lightbulb (variable load, even!) and an old school analog clock, and turn it on on. The LVD is repeatable, and so will always disconnect at the same voltage. Even if you don't have an ammeter, it's all relative. For big batteries (e.g., 50 Ah) , I use a 500 W halogen light - that's a 42A peak, 26A rms load. Smaller batteries, smaller bulb.
Anyway, set the clock to 12:00 (or something), and you don't even have to be there. Just return not too long after it shuts down, and recharge the battery. The clock will tell you exactly how long it ran under constant load.
I use this technique all the time. Very useful when evaluating batteries after desulphation, unknown batts, etc. Super easy, very repeatable, simple to vary the load. You do need the inverter, but those have many uses, and can be easy to borrow.
The CBA is also an excellent tool. But it's limited to 100 W (continuous), requires a PC, costs $100 ($600 for the 500 W expansion). If you need to balance $5000 worth of lithium, a great investment. But for less than $100, you also get an inverter you can use in your car (I know, but I bet most of us have one) to charge and/or run stuff. I use mine when camping - screw those propane or gas lanterns - run a CFL. Backpacking run LEDs.
Thoughts?
Plug in a lightbulb (variable load, even!) and an old school analog clock, and turn it on on. The LVD is repeatable, and so will always disconnect at the same voltage. Even if you don't have an ammeter, it's all relative. For big batteries (e.g., 50 Ah) , I use a 500 W halogen light - that's a 42A peak, 26A rms load. Smaller batteries, smaller bulb.
Anyway, set the clock to 12:00 (or something), and you don't even have to be there. Just return not too long after it shuts down, and recharge the battery. The clock will tell you exactly how long it ran under constant load.
I use this technique all the time. Very useful when evaluating batteries after desulphation, unknown batts, etc. Super easy, very repeatable, simple to vary the load. You do need the inverter, but those have many uses, and can be easy to borrow.
The CBA is also an excellent tool. But it's limited to 100 W (continuous), requires a PC, costs $100 ($600 for the 500 W expansion). If you need to balance $5000 worth of lithium, a great investment. But for less than $100, you also get an inverter you can use in your car (I know, but I bet most of us have one) to charge and/or run stuff. I use mine when camping - screw those propane or gas lanterns - run a CFL. Backpacking run LEDs.
Thoughts?
ort5
1 W
Nice trick Patrick. I especially like the clock!
I built a battery discharger using a similar setup, only using the coil voltage dropout point on a relay as the LVC on my system. You basically just make a voltage divider to set the cutoff point.
Got the idea from a friend here:
http://robot-club.com/teamtoad/bat-discharger.html
I built a battery discharger using a similar setup, only using the coil voltage dropout point on a relay as the LVC on my system. You basically just make a voltage divider to set the cutoff point.
Got the idea from a friend here:
http://robot-club.com/teamtoad/bat-discharger.html
safe
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Patrick said:
I've attempted to locate a seller for this with an internet search and am having troubles finding one. The search retrieves people talking about "HF multimeter" but no product references beyond that.
Could you get me a link to an online seller?HF Company(HF COMPANY). The Group's principal activity is to manufacture and sell signal transmission equipment. The Group offers terrestrial and satellite TV reception equipment such as cables, plugs, connectors, amplifiers and antennas. They offer digital peripheries such as interface boxes, wireless boxes, HIFI and IT equipment and GSM. The Group also offers home automation systems such as alarms, interphony and automatic doors. The Group is also involved in networking and offers signal processing equipment for high-speed network access on telephone lines. The Group markets its products under the brand names Lea, Avidson, Omenex, Kaorka and Extel. The Group operates mainly in Europe. In 2006, the Group acquired ACBS.
????
HF is HarborFreight. Try this link:
http://search.harborfreight.com/cpisearch/web/search.do?keyword=multimeter&Submit=Go
Although I see the least expensive meter is $5. Sometimes it's cheaper - I was in one of their stores last weekend and they had a pile for $3. Also, they have a pocket IR thermometer for $10 - it works pretty well, but only to about 230 F. But you probably don't want your motor/controller getting any hotter than this anyway.
Jameco also has several for under $20. The Vellemans seem ok.
http://search.harborfreight.com/cpisearch/web/search.do?keyword=multimeter&Submit=Go
Although I see the least expensive meter is $5. Sometimes it's cheaper - I was in one of their stores last weekend and they had a pile for $3. Also, they have a pocket IR thermometer for $10 - it works pretty well, but only to about 230 F. But you probably don't want your motor/controller getting any hotter than this anyway.
Jameco also has several for under $20. The Vellemans seem ok.
safe
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Patrick said:
This thread has gone all over the place, so I don't expect you to follow it all, but my original question was something more along the lines of:
"How can you beat a $10 load tester that also throws in the ability to measure the voltage?'
A standard multimeter doesn't do the load. I have a voltmeter already, but it's old and not very accurate. (I'm sure we abused it as kids... it's more of a historical item now since it was a WWII / Korean War relic)
I'll have to stock up on all this stuff, but I'm pretty sure now that my batteries are just getting old... when the weather drops below 85 degrees my old batteries just lose their "mojo". So I just have to wait and ride the bike next summer once the temperature rises again... (assuming they don't lose much more capacity during the winter) By next summer I'll have the Project #002 working and lose all interest in my old bike.
TylerDurden
100 GW
A cheap DMM is more useful. The load can be measured using the DMM and the lightbulb gag.safe said:
For $20 you can get the HF DMM that handles 20A and has temp sensing, cap checking and FET checking:
http://endless-sphere.com/forums/viewtopic.php?t=1867
safe
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TylerDurden said:
Run that "lightbulb gag" by me again...
How do you measure a current of say 60 - 100 amps with something like a regular DMM that is limited to 20 amps?
I'm kind of interested in this one because of the adjustable current capability. It's more expensive ($50) but for the MCL testing it might be nice to have something that is measuring the actual motor current that leaves the controller. You could remove the motor from the circuit and insert this to simulate the motor and set the "virtual current limit" to whatever you wanted and be certain of what was going on. Of course this is limited to 12 volts, so that's awkward...
I'm still undecided.
The load tester has a singular purpose of just testing you battery... it's not very flexible...
dirty_d
10 kW
well if you know the resistance of the load and the voltage across it then you know the current too, or you could buy a shunt or something with a known resistance to measure current. you could also buy a cheap analog ammeter, i have one on my bike monitoring motor current, it goes up to 50A and was $10 at electricscooterparts.com i think. the needle stays pegged to the max for a few seconds as i accelerate :lol:
safe
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I suspect this is what you were talking about. Yes, this looks good, and I recorded that link a long time ago as one of those "need to buy" items for the future. Maybe in the final analysis the easist thing to do is skip the multimeters and load testers and just buy the "on-the-bike" voltmeter and ammeter and try to debug the bike while riding. Ideally you want to do that sort of thing in a sort of lab environment where you can isolate all the variables, but running the simulations through testing machines could get expensive.
Maybe runtime testing is the easiest way to go?I'm sure Xyster would agree... he's a big supporter of "throttle fiddling" and "meter watching" while he rides.
I think what I might do is connect the voltmeter and ammeter to the motor side wires and then that way I can verify that the MCL circuit is working properly. Knowing the battery side values is not that important for what I'm planning to do. In fact, if it's possible to steal the signal output of the ammeter I might be able to use that as the input to the MCL circuit since that ammeter has a built in shunt. (that way I could avoid buying a Hall Effects sensor)
Question: Can you tell what the chances are for me to be able to dig inside that ammeter and get a signal to process?
dirty_d
10 kW
thats effectively the same as using a piece if wire as the shunt, that will work for measuring the battery side current but it makes the electronics a lot more complicated to do it like that for controlling motor side since the controllers ground is not at the same potential as the motor negative, the battery positive goes straight through the controller to the motor positive and the negative is switched. actually thats just my controller yours might be easier to work with, but the hall sensor would definitely be better, they're only $5 anyhow.
safe
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dirty_d said:
The thing is that I'll need to have a Hall Effects or Shunt anyway. It needs to be attached to the motor side wires, which on mine is simple enough because it's just a brushed motor. If it's possible to combine everything then I can rule out inconsistancies between measuring systems and maybe could reduce energy losses. The BEST thing would be to use a Hall Effects sensor and use that result to feed to an ammeter, thus eliminating the waste of using a shunt that you don't need. Maybe I could get a Hall Effects sensor that has very precise output and then have an LED that lights up at 10, 20, 30, 40, 50 or 60 amps. That way I could "tune" the system to an exact constant value and not have to worry about analog related problems.
It's all just design thoughts right now... and we're off topic...
I'll have to revive one of the "Motor Current Limiting" threads or make a new one specifically concerned with design.
safe
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Watt's Up about this Meter?
For $54.95 I could get:
"Measures up to eight DC values with much higher precision.
Amp-Hours: (0 - 65)
Watt-hours: (0 - 6554)
Amps: (0-100 peak)
Watts: (0 - 6554)
Peak Amps & peak Watts
Minimum voltage ("sags")
Voltage: (0 - 60)
Works with 12, 24, 36 or 48 volt batteries up to 60 V. Lead acid, SLA, Gel Cell, and other battery types are all compatible."
Seems like a better way to go than buying individaul voltmeters and ammeters and they have extra stuff too like the watt calculation, etc...
For $54.95 I could get:
"Measures up to eight DC values with much higher precision.
Amp-Hours: (0 - 65)
Watt-hours: (0 - 6554)
Amps: (0-100 peak)
Watts: (0 - 6554)
Peak Amps & peak Watts
Minimum voltage ("sags")
Voltage: (0 - 60)
Works with 12, 24, 36 or 48 volt batteries up to 60 V. Lead acid, SLA, Gel Cell, and other battery types are all compatible."
Seems like a better way to go than buying individaul voltmeters and ammeters and they have extra stuff too like the watt calculation, etc...
xyster
10 MW
The Watts-Up uses an internal shunt, which means big heavy power wires have to be run onto the handlebars and through the device. Also, 60V peak is far too low. What if you want to run 72V for project #004? Besides, its price would put you way over your stated budget.
The SickOAnalyst is well worth the extra dough if you're going to blow your budget anyway.
I like my cheap analog meters just fine. Though having an energy counter function for tracking battery capacity decline over time, and a little light for night riding would make the instrument cluster that much better.
The SickOAnalyst is well worth the extra dough if you're going to blow your budget anyway.
I like my cheap analog meters just fine. Though having an energy counter function for tracking battery capacity decline over time, and a little light for night riding would make the instrument cluster that much better.
safe
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xyster said:The Watts-Up uses an internal shunt, which means big heavy power wires have to be run onto the handlebars and through the device. Also, 60V peak is far too low. What if you want to run 72V for project #004? Besides, its price would put you way over your stated budget.
You get a shunt one way or another if you have an ammeter. I was imagining ways to circumvent that problem by using a Hall Effects sensor, but it seems like a lot of inventing for no good reason. At $55 this compares well to having to spend $25 for an ammeter and $25 for a voltmeter (or something like that) and it also helps me diagnose all the other stuff going on. This seems easy to implement.
As for mounting... I'd probably mount in on the frame in front of the forks where the top front fairing mounts would be. Like on the road racer motorcycles the instruments would be located inside the fairing and not on the handlebars. (with my weird bike this is where my battery wires come out of the frame)
As for voltage... the Project #002 was going to be a 48 volt machine. (the motor is only rated for 36 volts as it is) If I do something different for the one after that I'll buy new stuff for it. Somehow the idea of using a voltage above the level that causes death (above 50 volts) makes me feel a little uncomfortable...
TylerDurden
100 GW
safe said:
I wuz in HF yesterday and the DMMs were $2.85. A DMM can tell you everything you need to know (plus more)... you can do all the calculations in yer head while riding around in circles.
Eric G
1 kW
I just bought me one of those "Watt's Up" meters Safe and I think you could find it for a little cheaper if you hunt around a little.I got mine for $50.oo CDN shipping included. It seems rather versitile for various applications.You could use it to monitor the AH's going into the batteries while charging.Test load the batteries with the "light bulb gag".Fine tune riding habits with throttle/pedaling (although that one doesn't apply to your situation).
I just received mine in the mail yesterday and am a little excited about getting it into use.
Acomplete PDF manual can be found here...
http://www.powerwerx.com/techdata/Watts-UP-V2.pdf
Eric
I just received mine in the mail yesterday and am a little excited about getting it into use.
Acomplete PDF manual can be found here...
http://www.powerwerx.com/techdata/Watts-UP-V2.pdf
Eric
